Mitotic Dynamics of Normally and Mis-attached Chromosomes and Post-mitotic Behavior of Missegregated Chromosomes
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Equal segregation of the replicated genomic content to the two daughter cells is the major task of mitotic cells. The segregation is controlled by a complex system in the cell and relies mainly on the interaction between microtubules (MTs) of the mitotic spindle and kinetochores (KTs), specialized protein structures that assemble on each chromatid of each mitotic chromosome. By combining computational modeling and quantitative light microscopy, we established a quantitative model of the forces and regulators controlling metaphase chromosome movement in the mammalian cell line derived from Potorous tridactylis kidney epithelial cells (PtK1) (Chapter 2). This model can explain key features of metaphase chromosome dynamics and related chromosome structural changes experimentally observed. Moreover, the model made predictions, which we tested experimentally, on how changes in spindle dynamics affect certain aspects of chromosome structure. This quantitative model was next used to study the metaphase dynamics of chromosomes with erroneous KT-MT attachments (Chapter 3). Once again, the model predictions were tested experimentally and showed that erroneous KT-MT attachment alters the dynamics not only of the mis-attached KT, but also of its sister KT. Even more strikingly, experimental data showed that the presence of a single mis-attached KT could perturb the dynamics of all other, normally attached, KTs in anaphase. Chapter 3 also describe how MT poleward flux ensures correct KT-MT attachment and correct chromosome segregation. Indeed, reduced flux is associated with an increase in merotelically attached anaphase lagging chromosomes (LCs). These LCs form micronuclei (MNi) upon mitotic exit. The final effort of this work focused on the fate of MNi and micronuclated (MNed) cells (Chapter 4). Experimental observations showed that most of the chromosomes in MNi missegregated at the cell division following MN formation and that frequently the chromatin in the MN displayed delayed condensation. This work, thus, established a direct link between LCs and aneuploidy through the MN cell cycle.
- Doctoral Dissertations